The present invention relates to an image forming apparatus having a cleaning member or a transfer member which is brought into contact with and separated from an intermediate transfer member.
The present invention also relates to an image forming apparatus having a transfer roller which is brought into contact with and separated from an image carrying member and a mechanism for giving preliminary rotation to the transfer roller.
In image forming apparatus, toner images of four colors are sequentially formed on a photo conductor(s) and transferred to an intermediate transfer member so as to be superimposed one on another on the intermediate transfer member and are then transferred collectively to a sheet. The image forming apparatus includes a cleaning member and a secondary transfer roller that can contact and be separated from the intermediate transfer member. Remained toner is removed by the cleaning member after a transfer. (see JP-A-10-221967, JP-A-11-184203 and JP-A-2002-91107).
Also, another technique was proposed in which an endless belt is formed by joining the ends of an image transport belt together so as to produce a seam that is oblique with respect to the belt traveling direction to reduce the impact that occurs when a roller, cleaning blade, or the like goes over the seam (see JP-A-8-305112).
For example, in an image forming apparatus in which a color image is transferred to a transfer sheet by bringing a secondary transfer roller into contact with and separating it from an intermediate transfer belt for superimposition of images of different colors, the impact or impact-induced vibration that occurs when the secondary transfer roller contacts the intermediate transfer belt may disorder primary transfer images or move toner to cause a secondary transfer failure, resulting in an image formation failure. Toner and sheet material powder may be scattered by the impact or impact-induced vibration that occurs when the secondary transfer roller contacts the intermediate transfer belt, and may be suspended in the air. If suspended toner or sheet material powder sticks to a voltage application member surface of the intermediate transfer belt, the electric resistance varies there and the application voltage to the intermediate transfer belt is thereby varied, resulting in an image formation failure.
Further, unfixted toner held on the intermediate transfer belt by electrostatic absorption may be suspended in the air due to the impact that occurs when the secondary transfer roller contacts the intermediate transfer member. Suspended toner may stick to the voltage application member surface. Further, a transfer sheet that is transported being in pressure contact with the secondary transfer roller and the intermediate transfer belt may emit sheet material powder because of friction with the intermediate transfer belt during a secondary transfer or the transfer roller. Sheet material powder is generated most during a secondary transfer. Toner or sheet material powder tends to stick to the voltage application member surface in this manner. Where voltage application is effected by that member's contacting a contact-type voltage application member, a conduction failure occurs until passage of that portion.
Also, the above patent publications discloses the In image forming apparatus having the cleaning blade and the secondary transfer roller which are brought into contact with and separated from the intermediate transfer member. The cleaning blade and the secondary transfer roller are brought into contact with the intermediate transfer member by moving those from a state that they are separate from and parallel with the intermediate transfer member. However, vibration that is caused by the impact at the time of contact may cause suspension of toner in the air. Also, it may weaken the electrostatic absorption of toner by the intermediate transfer belt. This phenomenon has a particularly great influence on a belt-like intermediate transfer member having a seam as disclosed in JP-A-8-305112.
Also, when color superimposition is performed on the intermediate transfer member, the secondary transfer roller is separated from the intermediate transfer belt so as not to disorder images. The secondary transfer roller contacts the intermediate transfer belt only when images are transferred to a transfer medium. Since the secondary transfer roller is stopped when the secondary transfer roller contacts the intermediate transfer belt, the secondary transfer roller serves as a load of the rotation of the intermediate transfer belt until rotation speed of the secondary transfer roller coincides with the rotation speed of the intermediate transfer belt. The load is transmitted to the primary transfer section to disorder an image during a primary transfer or cause a color misregistration problem that a deviation occurs between the positions of images of a current color and a preceding color. To prevent these problems, a method disclosed in JP-B-3025070 was proposed in which the secondary transfer roller is driven at a lower speed than the intermediate transfer belt by using a one-way clutch, whereby the impact and the load at the time of contact are reduced.
The method proposed in JP-B-3025070 has the following problem. Since a driving system for driving the secondary transfer roller is provided, vibration in the secondary transfer roller driving system is transmitted to the intermediate transfer member, whereby slight density unevenness occurs in the primary transfer section. Further, since the secondary transfer roller is equipped with the one-way clutch and a drive gear that is engaged with the one-way clutch and the secondary transfer roller is brought into contact with and separated from the intermediate transfer member in such a manner that the one-way clutch and the drive gear operate simultaneously with the secondary transfer roller, the mass of the members that operate together with the secondary transfer roller is large. This results in a problem that the impact that occurs when the secondary transfer roller contacts the intermediate transfer member is strong and resulting vibration that is transmitted to the primary transfer section nay cause image density unevenness or color misregistration.